Process of varying the bitumen content of rock asphalt



H. "c, WOLF arch 3, 15936.

PROCESS OF VARYING THE BITUMEN CONTENT OF ROCK ASPHALT Filed Oct. 17, 1933 k ma? Gom I INVENTOR (M @Ww/W0? BY AT 17a RNEY Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE PROCESS OF VARYING THE BITUlVIEN CONTENT OF ROCK ASPHALT Application October 17, 1933, Serial No. 693,969

4 Claims.

It is Well known that there are a large number of natural deposits of rock asphalt throughout the United States. These natural rock asphalt beds are ordinarily classified under two major divisionsi. e., limestone base and those having a sandstone base. Both of the classes have a bituminous or asphaltic content which generally varies considerably, not only in content but also in type, in the different rock asphalt, even in a single bed. In some cases the bitumen content may be as high as 20% while in the poorer rock asphalt it may be as low as 5%.

The result of this variation is that it has been diilicult, if not impossible, to secure paving material from rock asphalt which would be uniform and produce high grade road pavement. For example, if the bitumen content is too high it invariably results that the paving made therefrom will soften and spread during hot weather while on the other hand if it has too small a content a brittle pavement will result. I have observed in practice, by investigation, analyses, and research tests, that the failure of pavements of this type is entirely due to the variation in the bitumen content of the natural rock asphalt and I have arrived at certain definite conclusions based upon these facts, viz:

First-That natural rock asphalt has not yet been duplicated synthetically because as yet there is no known method of reproducing within the limits of economical operation, the natural impregnation that is found in natural rock asphalt due to the long period of contact between the bituminous matter and the rock particle.

Second-As stated above, that the viscosity and mechanical characteristics of the bitumen content of the rock asphalt is of extreme importance in the Workability and lastingqualities of paving formed from this material.

Further that there is a very definite relationship existing between the chemical characteristics of the bitumen content of the rock asphalt and the mechanical characteristics of the same material when used for paving or roo-fing.

Further that a. variation of the asphalt-oil ratio in the bitumen will produce a variation in the characteristics in the rock asphalt so that by increasing the oil content up to 50% of the contained bitumen tends to increase the length of life of the paving made from rock asphalt such as is particularly reflected inthe fact that such rock asphalt paving will not become brittle nor will it crack with age.

Further that rock asphalt even from a single bed is seldom, if ever, uniformly coated as to each (Cl. 10G-31) particle; also that exudation of bitumen from the coated particles by passing the material through a zone of elevated temperature is not a reversible action when the temperature is lowered.

Due to these conclusions and facts determined in actual practice, I propose to provide a process which will utilize the foregoing discoveries in order to obtain a process for forming paving material which can be carried out continuously and will result in the production of a material of uniform excellence under all conditions of weather or temperature.

The object of my discovery is to produce a. process which, when followed, will ensure a pavement in which the bitumen content will be approximately uniform, at least sufciently uniform so that the quality of paving resulting from the use of the material will be Without substantial variation.

A further object of my invention is to provide as a step in the process of forming paving material from rock asphalt by which the bitumen content of the material is determined by color variation.

A further object is to provide means whereby the color variation of the material will automatically operate and control valves leading from supplies of material which will increase or decrease the bitumen content as may be required as indicated by the variation of color in the mass material.

Further objects will be apparent from the hereinafter contained description and may in part be pointed out hereinafter.

The process therefore consists of several steps, the relation and order of these steps with respect to one another of their order of use will be hereinafter described.

It will be perfectly apparent however, and I wish to be understood as stating, that certain steps may be omitted or may occur in altered relation to the other steps thereof.

For the purpose of conveying a graphic illustration of the discovery which I have made in this art I have attached to this specification and made a part thereof a graph which illustrates in detail several steps employed in utilizing my discovery.

As will be clear in viewing the drawing, the first step in my process is to grind, screen, pulverize,-wholly or in part-natural rock asphalt. In this manner I am enabled to materially increase the surface area thereof for the purpose of greater adsorption and absorption.

.bitumen content has been found to be within The next step is to dry this ground rock asphalt for the purpose of removing the moisture content whichV in practice has been found to be as high as 13% in the natural rock asphalt as it comes from the mines. I have found that where pavements made of rock asphalt have been laid, in which there is an excess of moisture and they have been exposed for some time to the heat of the sun and subjected to the various seasonal changes that they decompose and rot due to the excess of moisture found in the rock. It is well known that water has little affinity for the pitchy molecules of bitumen but rather destroys their cohesive qualities. The result is that Where an excess of moisture is present in the rock asphalt that the pavement deteriorates with great rapidity with the result that considerable fault is found With asphalt pavements which is not really due to the character of the pavement but rather to the fact that there is an excess moisture present inthe`rock`as it comes 'from the mine.

ThisV drying in my process may either be by stock piling or exposure to the air or by passing through any type of drier or heater which Will carrythe material through a zone of controlled elevated temperature.

In some cases it may be found desirable to expose the ground material to exposure to air to oxidize the light non-viscous hydro-carbons.

The ground material is then heated to a predeterminedtemperature condition in order to extract'the' surplus bitumen and to extract undesirable non-Viscous bitumen. This heat may be applied either by air such as natural heat or it may be mechanically applied in any convention- `al drier or heater. These temperatures may range from Fahrenheit to 450 Fahrenheit. I have found in practice that Fahrenheit is the most desirable for specific Kentucky rock asphalt for commercial production.

The material is then placed in a tumbler in which a temperature proper for exudation is maintained. This results in Vcoating all of the uncoated'particles with the exuded bitumen from the coated or saturated particles.

Provision should be made to control the temperature so as to secure uniformly coated particles and also for the purpose of drawing out the volatile portions or fractions of the bitumen. In this Way I obtain a mass of material in which 'each particle is uniformly coated with bitumen and in which the moisture content has been re- 'duced to the desired amount Vof approximately "photographs of the crystallized bituminous productor the crystallized sulpho or nitroso compound'of the bituminous content in order to aririve at a proper classification of the natural bituminous contents, such procedure tending to insure the correctresult of the process and the uniform quality of the product.

The objective of the chemical constituents of fairly close limit as follows:

Per cent Acids 2.3

Anhydrides 0.7 Asphaltines 19.5 Resins 24.7

Oils 49.5

all of which percentages are within the range of desirability. The sum of the group of the rst four should never exceed 65% of the total and it should not fall below 45% of the total, as I have observed in practice.

In practice I have found that the cohesive and adhesive characteristics, as well as the bitumen content of the processed rock asphalt each refleets in the finished material in a color variation, therefore when by observation the color of the finished material tends too strongly towards absolutely black, I add to the material any adsorbent or absorbent finely divided material in the order of clay, pulverized asphalt, pulverized grahamite, pulverized gilsonite, pulverized natural bitumen, pulverized carbon, pulverized activated carbon, pulverized carbonized rock asphalt or shales, pulverized fullers earth, pulverized silica or siliceous earth, or pulverized rock asphalt, for the purpose of adsorbing surplus bitumen or undesirable bitumen or any fraction `of thebitumen that is undesirable particularly light nonviscous fractions that may naturally be exuded or that may have been exuded by the processing. On the other hand should observation show that the color is too light as, Vfor example,`tending ing the viscosity and the above described chemical characteristic within the limits of desirability as above set forth. In practice, I prefer to use as raw material, rock asphalt having a natural bitumen content ranging from 5% to 6%, and

adding thereto bitumens in the form of asphalt, f

to the extent of 4% to 3%, respectively,V but the only objection to natural rock asphalt with a lower bitumen content is the economical objection of the cost of the added asphalt, and in practice, I have successfully used natural rock asphalt with a natural bitumen content as 10W as 3%, adding 61/2% of asphalt to such material. Experience indicates that the total percentage of bitumen, including the bitumen present in the natural raw rock asphalt, plus vthe bitumen in the Y added asphalt, should be between 9% and 10% in the final product, in most cases, but special usages have proven successful with final product bitumen vcontent ranging as low as 7% and as high as 13%. In no case, are the figures jquoted based on laboratory experiments, but in all cases, these percentages are based on actual practice of commercially laid paving materials.

It will be apparent to persons skilled in theY art that up to the present time I have described,

and set forth fully, a complete processV for the utilization of my discovery which will result in 'the production of a paving material of uniform quality and durability and excellence, recogniz-J ing, however, the desirability of removing the human equation to the fullest extent possible,

I have provided an additional step which may be employed when desired. This step is the control of the cohesive, adhesive and bitumen characteristic by the operation of photo-electric cellsA which are designed to automatically operate the valves and also to operate temperature controls in the exudation operation. As is well known photo-electric cells possess sensitivity to variation of light, i. e. color to a very high degree. Therefore if the color of the finished material tends too strongly towards absolute black the photo-electric cells affected thereby will operate temperature controls in ,the exudation step of the process which may have been stopped 'by 75 thermostatic controls, they will then also operate valve controls which are connected to a supply of asphaltic cement which is to be added, closing such valve or valves and in this manner reduce the percentage of asphaltic cement. Conversely if the color of the finished product tends too strongly towards brown or gray color the photo-electric cells Will operate to increase the temperature in the exudation phase of the operation within the thermostatic control set limit, after which the asphaltic cement valves are automatically opened and more asphaltic cement is thereby added.

From the foregoing it will be readily seen that I have set forth a concrete specic process for utilizing my discovery of a process to vary the bitumen content of rock asphalt for paving material by the color variation of the material itself but I do not desire to be understood as limiting myself to the precise order of these steps as described and as hereinbefore stated, I may find it desirable to omit some of these steps entirely or to alter their order for example, I may mix rock asphalt with the added asphaltic cement at atmospheric temperatures instead o1 elevated temperatures until a homogeneous mixture is obtained or I may add to rock asphalt before crushing, or after crushing, or after screening, or after exudation, or after heating, or after mixing before adding asphaltic cement, or after mixing after adding asphaltic cement, any adsorbent or absorbent finely divided material of the order of clay, pulverized asphalt, pulverized grahamite, pulverized gilsonite, pulverized natural bitumen, pulverized carbon, pulverized activated carbon, pulzerized carbonized rock asphalt or shales, pulverized fullers earth, pulverized silica or siliceous earth, or pulverized rock asphalt, such addition for the purpose of adsorbing surplus bitumen or undesirable bitument of any fraction of the bitumen that is undesirable, particularly light non-viscous fractions that may be naturally exuded, or that may have been exuded by the processing.

Having described my discovery what I regard as new and desire to secure by Letters Patent is:

1. The process of compounding a rock asphalt paving composition of a specied stability which consists of taking a rock asphalt whose principal ingredients are mineral matter and bitumen, reducing the same to a finely divided condition, reducing the moisture content in said nely divided material to approximately less than 1%, oxidizing light non-viscous hydrocarbons therein, heating said material to extract by exudation surplus bitumen, tumbling said material While at approximately the temperature of exudation, then selectively adding thereto an additional quantity of one of its ingredients and controlling the selection of said additional ingredient and the amount thereof by the light absorptive characteristics of rock asphalt so as to produce a stability equal to that of the specified stability.

2. The process of compounding a rock asphalt paving composition of a specied stability which consists of taking a rock asphalt whose principal ingredients are mineral matter and bitumen, reducing the same to a nely divided condition, reducing the moisture content in said nely divided material to approximately less than 1%, oxidizing light non-viscous hydrocarbons therein, heating said material to extract by exudation surplus bitumen, tumbling said material while at approximately the temperature of exudation, then selectively adding thereto an additional quantity of an adsorbent and controlling the selection of said additional ingredient and the amount thereof by the light absorption characteristics of said rock asphalt so as to produce a stability equal to that of the specified stability. 3. The process of compounding a rock .asphalt paving composition which consists of taking a rock asphalt Whose principal ingredients are mineral matter and bitumen, reducing the same to a finely divided condition, reducing the moisture content in said nely divided material to approximately less than 1%, oxidizing the light non-viscous hydrocarbons therein, heating said material to extract by exudation the surplus bitumen, then tumbling said material while maintaining it approximately at the temperature of exudation, then selectively adding thereto an additional quantity of one of its ingredients and controlling the selection of said additional ingredient and amount thereof by the light absorptive characteristics of said material while hot.

4. The process of compounding a rock asphalt paving composition Which consists of taking a rock asphalt Whose principal ingredients are mineral matter and bitumen, reducing the same to a nely divided condition, reducing the moisture content in said finely divided material to approximately less than 1%, oxidizing the light non-viscous hydrocarbons therein, heating said material to extract by exudation the surplus bitumen, then tumbling said material while maintaining it approximately at the temperature of exudation, then selectively .adding thereto an additional quantity of an adsorbent and controlling the selection of said additional ingredient and amount thereof by the light absorptive characteristics of said material While hot.

H. COMER WOLF. 

